sustitute is to replace a variable with a what ?

Answer 1

A value or expression.

Examples using 4x + 7:

substituting 3 for x: 4x + 7 = 4(3) + 7 = 12 + 7 = 19

substiuting 2x+ 1 for x: 4x + 7 = 4(2x + 1) + 7 = 8x + 2 + 7 = 8x + 9

Answer 2

Substitution is one of the fundamentals of algebra. Take this: a+2. What it means is that any number whatsoever can take the place of a, and what you do is that instead of writing in "a" put in the number instead, and do the same thing. So you are just replacing a with a value. (you are given what a is in a question)

e.g. What is a+2 where a is 5
So replace a with 5 i.e. 5+2
So is 7

I dont entirely know what you are actually asking, but hope that helped.

Answer 3

substitution means to replace a variable with the actual CONSTANT value of the variable or another way of expressing the same variable
for example
x=6 +y
10 +x + y=50
then substituting the value of x
10+6+y+y=50
16 +2y=50
2y=34
y=17

Answer 4

numbers only i believe